Braze repair of shroud block seal teeth in a gas turbine engine

ABSTRACT

An undersize repair region of a gas turbine engine stationary shroud is repaired with a sufficient mass of a repair material. The repair region includes a protruding portion that is undersized, and the repair includes machining of the protruding portion, grooving the resulting rub surface, inserting a replacement element, applying a brazing repair material, and brazing the article to form a repaired article. The repair material preferably includes a first fraction of a first powder of a first alloy component, and a second fraction of a second powder of a second alloy component. The first alloy component and the second alloy component have different solidus temperatures. The repair material is placed in the repair region. The repair material and the repair region are heated to melt the repair material but not the repair region, and thereafter the repair material and the repair region are cooled to solidify the repair material.

FIELD OF THE INVENTION

This invention relates to gas turbine engines and, more particularly, tothe repair of stationary shrouds found in gas turbine engines.

BACKGROUND OF THE INVENTION

In a gas turbine engine, air is drawn into the front of the engine,compressed by a shaft-mounted compressor, and mixed with fuel. Themixture is burned, and the hot combustion gases are passed through aturbine mounted on the same shaft. The flow of combustion gas turns theturbine by impingement against an airfoil section of the turbine bladesand vanes, which turns the shaft and provides power to the compressor.In aircraft applications, the hot exhaust gases flow from the back ofthe engine, driving the aircraft forwardly.

The turbine blades are mounted on a turbine disk, which rotates on ashaft inside a generally cylindrical tunnel defined by a hollowstationary shroud structure. The stationary shroud structure is formedof a series of stationary shrouds that extend around the circumferenceof the tunnel in an end-to-end fashion. The stationary shroud structurehas such a segmented arrangement to accommodate the thermal expansionexperienced during each engine cycle as the stationary shroud structureis cycled between room temperature and a maximum service temperature ofover 2000 degrees F. Each of the stationary shrouds has an internal gaspath surface that is a segment of a cylinder, and a support structurethat backs the gas path surface and provides for attachment to theadjacent structure. Additionally, in power generation applications, thegas path surface of the shrouds includes shroud block seal teeth thatprotrude from the shroud path surface. During turbine operation, theshroud block seal teeth act as a seal to minimize the escape of gasbetween the turbine blade and the shroud gas path surface.

During service, the shroud and the shroud seal teeth may be damaged byfatigue, erosion, and other mechanisms. One form of the damage is thewearing away of material from the shrouds, at locations such as the endfaces, the forward and aft edges, shroud teeth, and elsewhere. Asmaterial is worn away and during multiple repair cycles when material isremoved by machining operations, the shroud gradually becomes undersizein at least one dimension of the support structure and can provide apotential leak path for gas. When the shroud has become too small in atleast one dimension of the support structure to continue to befunctional, it is discarded.

There is a need for an improved approach to responding to damage to gasturbine engine shrouds, and particularly to protruding structures on thegas path face such as seal teeth. The shrouds are made of expensivenickel-base or cobalt-base superalloys, and the discarding of a shroudrepresents a substantial cost. The present invention fulfills this need,and further provides related advantages.

SUMMARY OF THE INVENTION

The present invention provides a method of repairing a protrudingstructure on a stationary shroud a gas turbine engine assembly. Therepair may be performed on any portions of the shroud structure. It ispreferably performed on the seal teeth which protrude from the shroudgas path face that faces the turbine blade tips in service, andgradually become undersized, chipped, or otherwise damaged. The repairedshroud is fully functional and is serviceable at a fraction of the costof a new shroud.

A method of repairing a gas turbine engine stationary shroud comprisesthe steps of providing the gas turbine engine stationary shroud havingan undersize repair region made of a shroud material, wherein the repairregion is located on a gas flow path surface of the gas turbine enginestationary shroud. The repair region can include, for example, aprotruding element such as an individual seal tooth, or a series ofindividual seal teeth, as well as the point of attachment of the base ofthe protruding element to the gas flow path surface. The repair regionof the gas turbine engine stationary shroud is repaired so that therepair region is no longer undersize.

The step of repairing includes the steps of machining at least oneprotruding element to be flush with the non-protruding gas path surfaceof the shroud, cutting a receiving groove or slot into the shroud gaspath surface, providing a replacement element and inserting thereplacement element into the receiving groove, and fixedly securing thereplacement element by brazing. Preferably, the step of repairingfurther includes the step of placing brazing material into the receivinggroove, and optionally also on the base of the protruding element andthe flow path face of the repair region. The step of brazing furtherincludes the steps of heating the repair material and the repair regionto a brazing temperature sufficient to melt the repair material but notthe replacement element or the shroud material of the repair region, sothat the repair material flows over the repair region to contact thereplacement element and the shroud, and thereafter cooling the meltedrepair material and the repair region to solidify the repair material.Additionally, the step of repairing can further include machining of therepaired shroud to restore desired dimensions.

The shroud material may be comprised of any metal or alloy suitable foruse in the high-temperature, highly oxidative environment of a gasturbine, including, but not limited to stainless steel, cobalt-basesuperalloys or a nickel-base superalloys, and the replacement element isalso preferably comprised of at least one of these materials. The brazerepair material is selected accordingly, and has a solidus temperatureless than that of the materials comprising the shroud and replacementelement.

The present approach achieves a fully serviceable repaired shroud,reducing the number of shrouds that are discarded. The scope of theinvention is not, however, limited to this preferred embodiment. Otherfeatures and advantages of the present invention will be apparent fromthe following more detailed description of the preferred embodiment,taken in conjunction with the accompanying drawings which illustrate, byway of example, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a turbine blade positioned adjacent to ashroud structure having protruding elements comprised of seal teeth.

FIG. 2 is an enlarged cross-sectional view of the shroud of FIG. 1.

FIG. 3 is a block flow diagram of one embodiment of the methods of thepresent invention.

Wherever possible, the same reference numbers will be used throughoutthe drawings to refer to the same or like parts.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 depicts a turbine blade 20 mounted to a periphery 22 of a turbinedisk 24. There are a large number of turbine blades 20 mounted in thisfashion to the turbine disk 24, but only one is illustrated. The turbinedisk 24 rotates on a turbine shaft (not shown) positioned along itscenterline. As the turbine disk 24 rotates, the turbine blade 20 sweepsthrough an annular volume between the turbine disk 24 and a stationaryshroud structure 26, a portion of the circumference of which is shownschematically in FIG. 1 and in more detail in FIG. 2. The shroudstructure 26 in its entirety defines a tunnel 28 in which the turbinedisk 24, turbine shaft, and turbine blades 20 rotate. Hot combustiongases flow from a combustor (not shown) through the annular volume ofthe tunnel 28 between the periphery 22 of the turbine disk 24 and theshroud structure 26, impinging against the turbine blades 20 and causingthe turbine disk 24 and the shaft to turn.

The shroud structure 26 is formed of a number of individual shrouds 30positioned in an end-to-end arrangement around the circumference of theblade tips to form a tunnel 28. One of the shrouds 30 is shown ingreater detail in FIG. 2. The shroud 30 has a gas flow path surface 32that faces the turbine blade 20. The shroud further includes at leastone protruding portion, such as one or more shroud seal teeth 33,provided on or attached to the shroud gas flow path surface 32 of theshroud 30. Seal teeth 33 are typically arranged circumferentially aroundthe gas flow path tunnel 28 formed by the shroud structure 26.Additional structural features, whose details and functions are notpertinent to the present invention, can include oppositely disposed endfaces that abut the end faces of any adjoining shrouds, an oppositelydisposed forward edge and aft edge, a back side that is opposite theflowpath face 32, and other common shroud features.

During service, one or more of the protruding features of the shroud 30,such as the seal teeth 33, may become damaged by removal of material, sothat the feature becomes undersized. For example, the seal teeth 33provided on the gas flow path surface 32 may become worn, or may chip orotherwise become damaged by contact with the turbine blade 20, foreignobjects, or simply from the force and heat of passing gasses. Initially,some such damage is acceptable, but eventually the feature is reduced insize so far below its desired specified service minimum dimension thatit is no longer functional. In the past, it has been the practice todiscard the entire shroud 30 at this point. The present inventionprovides a repair technique for the seal teeth 33 of the shroud 30 sothat the shroud 30 may be removed from the engine, repaired, and thenreturned to service.

FIG. 2 illustrates a gas turbine engine stationary shroud 30. The shroud30 has a repair region that is undersize. That is, some dimension of theshroud 30 is less than a specified service minimum dimension. Thecurrent repair region of most concern is loss of material from the sealteeth 33 that protrude from the gas flow path surface 32 since thisregion of the shroud experiences the greatest wear. As illustrated inFIG. 2, a specified service minimum dimension D, the protruding heightof the seal tooth 33, is indicative of the total protruding length ofthe seal tooth 33 as measured from the gas flow path surface 32 incontact with the base of the seal tooth 33. If D is too small, theshroud seal tooth 33 will be too short, and will not provide a properseal between the shroud 30 and the turbine blade, allowing turbine gasleakage between the shroud 30 and the turbine blade 20 and a resultingdecrease in operating efficiency.

FIG. 2 shows seal teeth 33 in various states of repair in accordancewith the present invention. For example, an intact seal tooth 33 of anew-make shroud, for example, is illustrated, a rub surface of theshroud 34 is shown, as well as a groove 35 for receiving a replacementelement 61 (here shown as a spad seal tooth). The shroud 30 and itsrepair region, in this case the repair region 36 that includes theprotruding seal teeth 33 and the surrounding gas flow surface 32, arerepaired by a technique involving removing, such as by machining away,the protruding seal teeth 33 to the non-protruding rub surface 34,cutting a receiving groove 35 below surface 32 in the gas flow pathsurface 32, inserting a replacement element 61 into the receiving groove35, and permanently affixing the replacement element 61 to the groove 35and the surrounding gas flow path surface 32 using a repair material 62.Preferably, the replacement element 61, here a spad tooth, includes afirst protruding end and a second opposite end configured for insertioninto the groove 35. More preferably, the groove 35 includes a bottomwall configured to securely receive the second end of the replacementelement 61, and can also include flanged sidewalls to allow repairmaterial to flow into any space between the walls of the groove 35 andthe replacement element 61 and the adjacent flow path surface 32 duringbrazing. Most preferably, the flow path surface 32 of the shroud 30 andrepair element 61 are made from the same material so as to ensurepredictable resistance to damage during brazing, and to ensuresubstantially uniform contact and adhesion properties in combinationwith the selected repair material 62 after brazing.

In the particular method of FIG. 3, the repair method includes the step70 of providing a stationary shroud 30 having a repair region 36. Therepair region includes at least one protruding element having adimension less than a specified service minimum dimension, such as aseal tooth 33. In step 72, the protruding element is removed to producea rub surface 34 that is substantially coplanar with the gas flow pathsurface 32. In step 74, a groove is cut into the flow path surface 32,preferably at the location of the rub surface 34 where the protrudingelement 33 was formerly located. Steps 72 and 74 can be performed as asingle operation, if desired. In steps 76 and 78, respectively, a repairmaterial 62 and a replacement element are provided. In step 80, thebraze repair material is placed into the repair region 36 in proximityto the groove 35. In step 82, a replacement element such as a seal tooth33, is placed into the groove 35. In step 84, the repair region isheated to a brazing temperature, wherein at least a portion of the brazerepair material 62 is melted and contacts the flow path surface 32 andthe replacement element 61, and preferably the walls of the groove 35.Some braze material may be located in groove 35. However, this is notfundamentally necessary if the tooth 33 is fitted into groove 35 so thatthere is a space between the walls of groove 35 and surfaces of tooth33. In this circumstance, the molten braze material will flow into thespace by capillary action. In step numeral 86, the repair region 36 isallowed to cool, thereby solidifying the brazed repair material 62 tosecurely adhere the replacement element 61 to the shroud 30. Optionally,the method further includes the additional step numeral 88 of machiningthe repair region, including the repair material 62 and replacementelement 61, to restore dimensions appropriate for service in the gasturbine engine.

The repair material 62 is a braze material that is selected to becompatible with the material of the shroud 30 and the replacementelement 61. The brazing material can be provided in the form of wire,rod, strip, foil, powder, and/or a viscous mixture (paste) includingpowder in a suitable binder. Where the shroud 30 and/or replacementelement are comprised of stainless steel, the repair material 62 ispreferably a nickel alloy brazing material. More preferably, the shroudis made of 310 stainless steel or 410 stainless steel, and the brazingmaterial is a nickel alloy brazing filler. Most preferably, the brazingfiller is comprised of about 82% Ni, 4.5% Si, 7.0% Cr 3.1% B, 3.0% Fe,and characterized by a solidus-liquidus range of between about 1780 toabout 1830° F. (about 971 to about 999° C.). An exemplary nickel alloybrazing material having these properties is SAE AMS4777F, as specified,described and published by the Society of Automotive Engineers, Inc. ofWarrendale, Pa., USA. However, other nickel alloy brazing materials canbe utilized. In this embodiment, the preferred nickel alloy brazingmaterial is capable of joining nonferrous alloys and corrosion and heatresistant steels and alloys, and displays low flow point and corrosionand oxidation resistant joints with good strength at elevatedtemperatures. A further benefit of the preferred nickel alloy brazingmaterial is that it provides a corrosion and oxidation resistant hardcoating that can be smoothed and otherwise worked to yield a smoothrepair area on turbine engine components that are routinely exposed tohigh operating temperatures. Because the braze material includes Boron,an element that diffuses very rapidly, and Si, an element that diffusesquickly (but not as quickly as Boron), these elements, which contributeto the solidus temperature of the braze material being lower than thematerials being joined, will rapidly diffuse from the braze materialupon high temperature exposure, thereby raising the solidus temperatureof the braze material.

Alternatively, where the material comprising the shroud and/or repairelement 61 is an alloy, such as a cobalt-based superalloy or anickel-based superalloy, an appropriate repair material 62 can beselected according to the alloy material. Appropriate braze materialsand methods for such alloys are disclosed in commonly owned U.S. Pat.No. 6,464,128, which is hereby incorporated by reference. For example,in one embodiment, the repair material 62 is a braze material comprisinga powder of a first alloy component and a powder of a second alloycomponent, each component having different solidus temperatures. Therepair material that is later formed as a melted mixture of the firstpowder and the second powder has a solidus temperature less than that ofa shroud material that forms the repair region 36. In this embodiment,the first powder and the second powder are selected according to theshroud material that forms the repair region, as well as the materialthat forms the replacement element 61, such as a spad seal tooth 33. Thepowders selected for cobalt-base shroud materials are different fromthose selected for nickel-base shroud materials. In a case of particularinterest, the shroud material is a cobalt-base alloy known as Mar M509,which has a nominal composition, in weight percent, comprising about23.5 percent chromium, about 10 weight percent nickel, about 7 percenttungsten, about 3.5 percent tantalum, about 0.2 percent titanium, about0.4 percent zirconium, about 0.6 percent carbon, no more than about 2percent iron, the balance cobalt and impurities. Additionally, the brazerepair material can include melt-depressants such as Boron and Silicon.

For cobalt-base shroud and replacement element material, the first alloycomponent of the repair material 62 preferably comprises a prealloyedcomposition, in weight percent, of from about 10 to about 25 percentnickel, from about 15 to about 25 percent chromium, from about 5 toabout 10 percent silicon, from about 2 to about 6 percent tungsten, fromabout 0.2 to about 0.8 percent carbon, from about 0.4 to about 2.0percent boron, balance cobalt and impurities. The second alloy componentpreferably comprises a prealloyed composition, in weight percent of fromabout 5 to about 15 percent nickel, from about 15 to about 30 percentchromium, about 2.0 percent maximum silicon, from about 5 to about 10percent tungsten, from about 0.3 to about 0.8 percent carbon, about 1.5percent maximum manganese, about 3 percent maximum iron, about 0.5percent maximum zirconium, balance cobalt and impurities. The firstfraction is preferably from about 25 weight percent to about 50 weightpercent, most preferably about 35 weight percent. The second fraction ispreferably from about 75 weight percent to about 50 weight percent, mostpreferably about 65 weight percent.

On the other hand, the shroud 30 and replacement element 61 can beinclude a nickel-base superalloy such as Rene N5, which has a nominalcomposition, in weight percent, of from about 6 to about 6.4 percentaluminum, from about 6.75 to about 7.25 percent chromium, from about 7to about 8 percent cobalt, from about 0.12 to about 0.18 percenthafnium, from about 1.3 to about 1.7 percent molybdenum, from about 2.75to about 3.25 percent rhenium, from about 6.3 to about 6.7 percenttantalum, from about 4.75 to about 5.25 percent tungsten, a sum ofaluminum plus tantalum about 12.45 percent minimum, balance nickel andimpurities. Where the shroud material is a nickel-base superalloy suchas Rene N5, the first alloy component preferably comprises a prealloyedcomposition, in weight percent, of from about 10 to about 20 percentcobalt, from about 14 to about 25 percent chromium, from about 2 toabout 12 percent aluminum, from 0 to about 0.2 percent yttrium, balancenickel and impurities. The second alloy component preferably comprises aprealloyed composition, in weight percent of from about 10 to about 20percent cobalt, from about 14 to about 25 percent chromium, from about 2to about 12 percent aluminum, from about 2 to about 12 percent silicon,balance nickel and impurities. The first fraction is preferably fromabout 55 to about 80 weight percent, most preferably about 68.5 weightpercent. The second fraction is preferably from about 45 weight percentto about 20 weight percent, most preferably about 31.5 weight percent.

Where the repair material 62 is comprised of two types of individuallyprealloyed powders, the powders may be provided in a loose, free-flowingform. Alternatively, they may instead be provided as an unsinteredcompact or a pre-sintered compact. Both approaches are operable,although the use of the pre-sintered compact can be more practical forproduction operations. In this latter approach, the powders are mixedtogether, pressed with a binder into a desired shape before applying tothe repair region. Optionally, to form a pre-sinter, the mixed powderscan be pre-sintered by heating to a temperature where the powders areslightly sintered together to form a compact. It is not necessary thateither compact have a high relative density (that is, little porosity),as it is later fully melted. The compacts are more easily handled andpositioned than are the free-flowing powders, and there is lesscompaction and shrinkage in subsequent melting. A combination of theseapproaches may be desired. For example, a compact may be contacted tothe flow path surface 32, and free-flowing powders may be packed intothe groove 35.

The braze repair material 62 is placed into the repair region 36. Therepair material 62 may be the mixture of the free-flowing powders, thecompact, or a combination of both. The amount of braze repair material62 is preferably selected so that, after subsequent melting andmachining, the gas flow path surface 32, the replacement element 61, andthe rest of the repair region is restored to approximate a predetermineddesired service dimension. However, machining can be performed as anadditional step to impart and restore desired dimensions of the surface32, replacement element 61, and other features within the repair region36 if desired.

The replacement element 61 is placed in the groove 35, and the repairmaterial 62 within the repair region 36 is heated to a brazingtemperature to melt at least a portion of the repair material but notthe shroud material or replacement element 61 of the repair region. Thebraze repair material 62 should always be selected so that its meltingtemperature is below both that of the replacement element 61 and shroudbase material 30. In the case of the above-discussed preferred repairmaterial for stainless steel shrouds 30 and replacement elements 61, thebrazing temperature is between about 1780 degrees F. to about 1830degrees F. However, the brazing temperature can be varied between about1400 and about 2200 degrees F. based on parameters of the particularrepair, including mass, configuration, and application.

Where the shroud 30 and replacement element 61 are comprised ofcobalt-base alloys or the nickel-base alloys, the brazing temperature isfrom about 2190 degrees F. to about 2335 degrees F., and preferably fromabout 2300 degrees F. to about 2325 degrees F. However, the brazingtemperature range can be further varied based on parameters of theparticular repair, including mass, configuration, and application. Inembodiments wherein the repair material includes two alloy powders, atthe brazing temperature, the powder having the lower solidus temperaturemelts to accelerate the bonding to the shroud 30 and replacement element61 and the densification process, while the powder having the highersolidus temperature remains solid so that the powder mass generallyretains its shape.

The brazing is preferably performed in a vacuum furnace. The brazingtime, defined as the period of time at which the repair region 36 ismaintained at a temperature sufficient to braze the repair material 61,can also be varied based on parameters of the particular repair,including mass, configuration, and application. For example, the brazingtime is typically on the order of about 20 minutes to about 2 hours.More preferably, the brazing time is between about 1 hour to about 2hours. After brazing, the repaired workpiece is braze cooled to solidifythe repair material. The braze repair material solidifies, forming ametallurgical bond to the shroud 30 and the replacement element 61. Theresult is a repaired article having a replacement element 61 permanentlyaffixed to the repair region of the shroud 30. In most cases, the amountof braze repair material is selected so that the repair region will beslightly oversize after the brazing and cooling steps. Although it wouldbe desirable to make the repair exactly the right size after brazing andcooling, it is typically not possible to control the amount anddistribution of the repair metal that precisely. Accordingly, the repairregion can be made oversize, and then excess material machined away toachieve the correct size and with the necessary details to restore therepair region to operating tolerances.

While the invention has been described with reference to a preferredembodiment, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims.

1. A method of repairing a gas turbine engine stationary shroud, themethod comprising the steps of: providing the gas turbine enginestationary shroud having an undersize repair region made of a shroudmaterial, wherein the repair region is a protruding element located on agas flow path surface of the gas turbine engine stationary shroud;repairing the repair region of the gas turbine engine stationary shroudso that the repair region is no longer undersize, further including thesteps of: removing the protruding element from the shroud; forming areceiving groove in the repair region, the groove extending below thegas flow path surface; placing a replacement element into the receivinggroove; placing a braze repair material in the repair region, the brazerepair material having a solidus temperature less than that of theshroud material; heating the repair region, the replacement element, andthe repair material to a brazing temperature sufficient to melt at leasta portion of the braze repair material but not the replacement elementor shroud material of the repair region, so that the repair materialflows over the repair region, into the groove, contacting thereplacement element and the gas flow surface; and thereafter cooling themelted braze repair material and the repair region to solidify the brazerepair material.
 2. The method of claim 1, wherein the step of providingthe gas turbine engine stationary shroud includes the step of providingthe repair region having a protruding element dimension less than aspecified service minimum dimension.
 3. The method of claim 1, whereinthe step of placing a repair material in the repair region includesplacing the repair material in the receiving groove.
 4. The method ofclaim 1, wherein the step of providing a gas turbine engine stationaryshroud includes the step of providing a gas turbine engine stationaryshroud wherein the shroud material comprises stainless steel.
 5. Themethod of claim 4, wherein the step of placing a braze repair materialinto the repair region further includes the step of providing a brazerepair material comprising nickel, chromium, and iron and a meltdepressant element.
 6. The method of claim 5, wherein the braze repairmaterial is comprised, in weight percent, of about 82 percent nickel,about 4.5 percent silicone, about 7.0 percent chromium, about 3.1percent boron, and about 3.0 percent iron.
 7. The method of claim 1,wherein the step of providing a gas turbine engine stationary shroudincludes the step of providing a gas turbine engine stationary shroudwherein the shroud material comprises a cobalt-base alloy.
 8. The methodof claim 7, wherein the cobalt base alloy has a composition, in weightpercent, comprising about 23.5 percent chromium, about 10 weight percentnickel, about 7 percent tungsten, about 3.5 percent tantalum, about 0.2percent titanium, about 0.4 percent zirconium, about 0.6 percent carbon,no more than about 2 percent iron, balance cobalt and impurities.
 9. Themethod of claim 8, wherein the braze repair material is comprised of amixture of two alloy components, each comprising a weight fraction ofthe total braze material mixture and wherein the first alloy componentcomprises a prealloyed composition, in weight percent, of from about 10to about 25 percent nickel, from about 15 to about 25 percent chromium,from about 5 to about 10 percent silicon, from about 2 to about 6percent tungsten, from about 0.2 to about 0.8 percent carbon, from about0.4 to about 2.0 percent boron, balance cobalt and impurities, and thesecond alloy component comprises a prealloyed composition, in weightpercent of from about 5 to about 15 percent nickel, from about 15 toabout 30 percent chromium, about 2.0 percent maximum silicon, from about5 to about 10 percent tungsten, from about 0.3 to about 0.8 percentcarbon, about 1.5 percent maximum manganese, about 3 percent maximumiron, about 0.5 percent maximum zirconium, balance cobalt andimpurities.
 10. The method of claim 9, wherein the first alloy componentcomprises about 25 weight percent to about 50 weight percent, and thesecond fraction comprises the balance.
 11. The method of claim 1,wherein the step of providing a gas turbine engine stationary shroudincludes the step of providing a gas turbine engine stationary shroudmade of a shroud material comprising a nickel-base superalloy.
 12. Themethod of claim 11, wherein the braze repair material is comprised of amixture of two alloy components, each comprising a weight fraction ofthe total braze material mixture.
 13. The method of claim 12, whereinthe first alloy component comprises a prealloyed composition, in weightpercent, of from about 10 to about 20 percent cobalt, from about 14 toabout 25 percent chromium, from about 2 to about 12 percent aluminum,from 0 to about 0.2 percent yttrium, balance nickel and impurities, andthe second alloy component comprises a prealloyed composition, in weightpercent of from about 10 to about 20 percent cobalt, from about 14 toabout 25 percent chromium, from about 2 to about 12 percent aluminum,from about 2 to about 12 percent silicon, balance nickel and impurities.14. The method of claim 13, wherein the first alloy component is fromabout 55 to about 80 weight percent, and the second alloy component isfrom about 45 weight percent to about 20 weight percent.
 15. The methodof claim 1, wherein the repair region is a seal tooth of the gas turbineengine stationary shroud.
 16. The method of claim 1, wherein the step ofplacing a repair material into the repair region further includes thestep of providing the braze repair material as a free-flowing powder.17. The method of claim 1, wherein the step of placing a repair materialinto the repair region further includes the step of providing the repairmaterial as a sintered compact.
 18. A method of repairing an articlehaving a protruding portion extending partially into a flow path surfacein a gas turbine engine, the article previously exposed to hightemperature operation in the gas turbine engine, the method comprisingthe steps of: identifying an undersize dimension of the protrudingportion of the article, the undersize dimension being less than aspecified minimum service dimension and the undersize dimension beingdefined at least in part by a flow path surface of the article;machining the protruding portion to form a non-protruding rub surface;forming a groove in the non-protruding rub surface extending below therub surface; providing a repair element having a protruding portion andan opposite portion configured for insertion into the groove; providinga braze repair material; applying the braze repair material to therepair element and to the to the rub surface; heating the braze repairmaterial and the article to a brazing temperature above the meltingtemperature of the braze material sufficient to melt at least a portionof the repair material but below the melting temperature of the articleand the replacement element; and cooling the braze repair material andthe repair region to solidify the braze repair material, the solidifiedrepair material increasing the undersize dimension.
 19. The method ofclaim 18, further comprised of the step of machining the repairedarticle to yield a repaired article having dimensions appropriate forservice in the gas turbine engine.